Lead borosilicate glass

Figure 2-1 Curves for linear shrinkage rate (a) and curves for activation energy (b) in alumina/lead borosilicate glass composites at different programming rates [Ref. 10, 11].

The resistance of a cermet film is determined by the metal-to-glass ratio. For example, the resistance of lead-borosilicate glass and either Ag or Au changes by five orders of magnitude with a few percent change in metal content (see Fig. 2.56), whereas either Pd or Pd -I-Ag glass mixtures are much less sensitive therefore, they are more easily reproduced on a production basis. The addition of silver to palladium improves the temperature coefficient of resistance and decreases the electrical noise and resistivity of the films (see Table 2.23). 

TABLE 8.19 Physical Properties of Typical Lead Borosilicate Glass... 

For the soda-Hme-silica glasses this is about 2-5 gm/cm for the borosilicate glasses it is very nearly 2-25 gm/cm and hardly changes with slight variations in composition. Wembley L.l. lead glass has a density of 3-08. A very dense lead glass has a density of 5-2. 

An interesting example of the contamination risks which may be caused by a laboratory vessel is that of boron. Determination of very low boron concentrations, involves a prior separation by distillation and subsequent analysis by spectrometry, with a suitable reagent such a curcumin or carminic acid. The use of laboratory vessels made of borosilicate glass (such as Duran or Pyrex) could lead to very large errors in the boron content found. Such errors are caused by sample contamination from the boron present in the glassware. 

The environment and oxidation state of iron in borosilicate glasses has been probed by IR, Raman, and Mossbauer spectroscopies, in lead vanadate (Pb2V207) glasses by XRD and IR and Raman spectroscopies. " ... 

Figure 7. Radiation shielding window showing Ce-stabilized borosilicate glass cover plates (RS 253 G 18) on the hot side, stabilized lead glass (RS 323 G 15), nonstabilized high density lead glass (RS 520) and borosilicate glass cover plate...

Fig. 3.20. Common conductivity probe for vacuum work. A couplings to shielded cables from conductivity meter 5 a B. 19 or B.24 socket fitting onto cone on observation/reaction vessel C graded-seal soda glass to borosilicate glass D shielded leads spot-welded to thick Pt wires E sealed through the soda glass probe and held together by the lead glass bead F.

Fig. 3.22. Arrangement of the leads inside the conductivity cell shown in Fig. 3.23. Cu copper wire, Sd soldered joint, W tungsten wire, SW spot-weld, Pt platinum wire, S soda glass sleeve, SS silver-soldered joint, P borosilicate glass arm fused to the cell, PtP platinum plate electrodes held together with lead glass beads L.

Fig. 3.25. The Pask-Nuyken device for measuring simultaneously the conductivity and the UV spectrum of a reaction mixture. A mixing chamber, B conductivity cell with jacket, C graded-seal borosilicate glass-soda glass, D jacketed quartz cell, E copper leads to platinum electrodes Pt, F graded-seal borosilicate glass-quartz.

For both type of microwave reactors, if the reactor is not supplied with a temperature sensor or more likely accurate temperature measurment is prerequisited during an experiment, the fiber-optic temperature sensor is directly applied to the reaction mixture. In order to secure the sensor from harsh chemicals, the sensor is inserted into a capillary that in turn is inserted into the reaction mixture. In such a case, it is strongly advocated to use capillaries that are made of quartz glass and are transparent to microwave irradiation. Any capillary that is made of glass or even borosilicate glass can always slightly absorb microwave energy, in particular, while the reaction mixture does not absorb microwaves efficiently, and in turn lead to failures of fiber-optic thermometer performance. 

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